down home has it right. Assuming access to plumbing and sewage, why not leave the grey tank dump valve open (not the black), and route a dehumdifier's drain to the bathtub or a sink (making sure the sink drains to the grey... some bathroom sinks drain to the black tank.) That would take care of the humidity in the rig.
I'd probably leave both A/Cs on a temperature like 80 as described above, if only just to exercise them so the compressors stay active and don't seize.
The black tank, I'd dump, rinse, then pour a gallon or two of RV antifreeze in there. RV antifreeze won't evaporate, so it will keep things in the tank from turning to "stone". I'd also pour RV antifreeze down the sinks and tub as well to keep gases out of the coach area.
Battery, I'd check to make sure you have a three stage RV converter. If a single stage, chuck it and get a better model with Charge Wizard-like functionality, which will trickle charge batteries when near 100% charged. A single stage converter will boil the battery in no time.
Water, I'd disconnect and leave disconnected. That way, if something would spring a leak, you don't have a flood when gone. I'd also drain the tanks and run the pump dry so there is less water that turns to algae while gone.
Refrigerator, up to you. I'd probably fill up the propane tanks and run it on gas while gone (a propane fridge will go through a 20# bottle in about 30 days), which will keep the spiders out of the flue. Cheap insurance, since an insect infestation can get expensive. Just remember that the fridge does use 12 volts, even on propane so it will drain the battery dry in a week or two unless it is being charged somehow (shore power, solar, etc.)
Oh, don't forget to put screens on the furnace, fridge vents, water heater, and other items... otherwise, you might find some hornet nests or mud dauber wasps have made themselves home in there.
